What Exactly are diamonds?
Diamond is carbon in its most concentrated form. Except
for trace impurities like boron and nitrogen, diamond
is composed solely of carbon, the chemical element that
is fundamental to all life. But diamond is distinctly
different from its close cousins the common mineral
graphite and lonsdaleite, both of which are also composed
of carbon. Why is diamond the hardest surface known
while graphite is exceedingly soft? Why is diamond transparent
while graphite is opaque and metallic black? What is
it that makes diamond so unique?

The key to these questions lie in diamond's particular
arrangement of carbon atoms or its crystal structure--the
feature that defines any mineral's fundamental properties.
A crystal is a solid body formed from the bonding of
atomic elements or compounds in a repeating arrangement.
Often, crystals possess smooth external faces. Due to
their symmetrical and finite nature, the building blocks
of crystals are limited to relatively small numbers
of atoms, and their chemical compositions to simple
numerical combinations of elements.